När ska vilka måttenheter användas i CSS? →

Amidst the diversity of CSS measurement systems it can be difficult for web developers to understand which units to use where, and when, on their pages. The instinct is to use just one system for everything, but that decision can severely limit the execution of your designs.

What follows is a list of suggestions, not absolute rules. If you have a differing opinion or working practice (and a rationale to back it up), please share in the comments.